1. Field of the Invention
The present invention relates to a forced flue type combustion device which has a combustion chamber incorporating a burner, an air supply passage for supplying combustion air to the interior of the combustion chamber, an exhaust passage for discharging flue gas in the combustion chamber generated by combustion with a burner, and a combustion fan interposed in one of the air supply passage and the exhaust passage, and in which combustion air is forcibly supplied to the interior of the combustion chamber by the rotation of the combustion fan, while flue gas in the combustion chamber is forcibly exhausted out of the combustion chamber by the rotation of the combustion fan.
2. Description of the Related Art
When the air supply passage or the exhaust passage in this kind of combustion device clogs, the rate at which combustion air supplied to the combustion chamber is reduced relative to that corresponding to the rotational speed of the combustion fan, resulting in incomplete combustion due to deficiency of air.
A forced flue type combustion device is hitherto known which is designed to avoid this problem and which has an orifice provided in at least one of the air supply passage and the exhaust passage, a pressure difference sensor for detecting the difference between the gas pressure on the upstream side of the orifice and the gas pressure on the downstream side of the orifice, and a clogging determination elements configured to determine whether or not the air supply passage and/or the exhaust passage is clogged on the basis of the detected pressure difference value from pressure difference sensor (see, for example, Japanese Patent Laid-Open No. 2000-310419). The difference between the gas pressure on the upstream side of the orifice and the gas pressure on the downstream side of the orifice changes according to the rate of flow of gas through the orifice. Therefore, when the air supply passage or the exhaust passage is clogged so that the gas flow rate is reduced, the detected pressure difference value from the pressure difference sensor is reduced. Thus, it is possible to determine the existence/nonexistence of a clog on the base of the detected pressure difference value by the clogging determination elements. When it is determined that the passage is clogged, the combustion with the burner is stopped to prevent the occurrence of incomplete combustion.
Since the rotational speed of the combustion fan is reduced during weak combustion with the burner, the rate at which gas flows through the orifice is reduced to a small value even in a normal state in which each of the air supply passage and the exhaust passage is not clogged. During weak combustion, therefore, the amount of change in the detected pressure difference value between normal and clogged states is extremely small and the existence/nonexistence of a clog cannot be determined with accuracy.